Tape volume overwrite protection during error recovery

ABSTRACT

An apparatus-implemented method according to one embodiment includes detecting an error while writing data to a tape volume on a tape and repositioning the tape in response to detecting the error. A determination whether a rewrite of data associated with the error to the tape volume is allowed is made based on a current position of the tape after the repositioning. The data is rewritten to the tape volume in response to determining that the rewrite of data associated with the error to the tape volume is allowed. A computer program product for protecting overwrite of a tape volume according to another embodiment includes a computer readable storage medium having program instructions embodied therewith, the program instructions readable and/or executable by a controller to cause the controller to perform the foregoing method.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to preventing data overwrite duringerror recovery.

During write operations to a physical or virtual tape volume, errors mayoccur that require repositioning a write head to a prior position on thetape volume. As a result of the repositioning, the write head may bepositioned over previously written data, such as at the beginning of thetape volume. Under some circumstances, the write head may resume writingoperations to the tape volume while still positioned over the previouslywritten data, resulting in an overwrite of the previously written data.Unfortunately, the data may be lost as a result of the overwriting.

Depending on the circumstances of the overwrite, and the type of thetape volume, recovery of the data may be possible. However, in othercircumstances the overwrite will result an actual loss of the data. Thismay be especially true in a disk-only virtual tape environment, becauseany write attempt at the beginning of the volume will cause a disk filerepresenting the tape volume to be truncated. In such situations, anyability to recover the overwritten data may then depend on other backupsthat exist, such as on other disks and/or tapes. Even when other backupsdo exist, recovering lost data often consumes a significant amount oftime and effort.

SUMMARY

An apparatus-implemented method according to one embodiment includesdetecting an error while writing data to a tape volume on a tape andrepositioning the tape in response to detecting the error. Adetermination whether a rewrite of data associated with the error to thetape volume is allowed is made based on a current position of the tapeafter the repositioning. The data is rewritten to the tape volume inresponse to determining that the rewrite of data associated with theerror to the tape volume is allowed.

A computer program product for protecting overwrite of a tape volumeaccording to another embodiment includes a computer readable storagemedium having program instructions embodied therewith, the programinstructions readable and/or executable by a controller to cause thecontroller to perform the foregoing method.

An apparatus-implemented method, according to yet another embodimentincludes detecting an error while writing data to a tape volume,receiving a positional indicator, repositioning the tape in response todetecting the error, determining a current position of the tape afterthe repositioning, and determining whether a rewrite of data associatedwith the error to the tape volume is allowed based on a comparison ofthe current position of the tape to the positional indicator.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head. Further, any of these embodiments may be implemented in avirtualized tape system.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration example of system utilizinga tape drive, in accordance with one embodiment.

FIG. 2 is an illustration of a tape drive, in accordance with anembodiment.

FIG. 3 illustrates a method for tape volume overwrite protection duringerror recovery, according to one embodiment.

FIG. 4 is a diagrammatic representation of a tape volume, in accordancewith one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof. For example, various embodiments disclosed herein are able toprevent overwriting of data stored to a tape volume. In variousembodiments, upon receiving a write command, a tape drive describedbelow may only allow the write to a tape volume if a write head ispositioned at an acceptable location on the tape volume, e.g., toprevent any unwanted overwrite of data resulting from a prior tapevolume rewind.

In one general embodiment, a method includes detecting an error whilewriting data to a tape volume, repositioning the tape volume forrecovering from the error, and receiving, after the repositioning, atleast a portion of the data for rewriting the at least a portion of thedata to the tape volume. Further, the method includes determining, afterthe repositioning, a current position of the tape volume, anddetermining, based on the current position of the tape volume, whetherthe rewrite to the tape volume is allowed.

In another general embodiment, a system includes a processor and logicintegrated with and/or executable by the processor. The logic isconfigured to cause the foregoing method to occur.

In yet another general embodiment, a computer program product includes acomputer readable storage medium having program instructions embodiedtherewith, the program instructions readable and/or executable by acontroller to cause the controller to perform the foregoing method.

Various embodiments may be implemented in a standalone system, such asin a tape drive that may be coupled to a host. In other approaches, thesystem may be implemented in an automated data storage library or avirtual tape volume.

Referring now to FIG. 1, an exemplary configuration of an operatingenvironment 100 is shown. The operating environment 100 is configured toinclude a tape drive 10, a host (server) 30, and PCs (terminals) 32, 34,which are communicable with one another through a network 36. The tapedrive 10 and the host (server) 30 are each illustrated as one componentin FIG. 1, but this is just an example. Two or more tape drives 10 andhosts (servers) 30 may be included.

FIG. 2 is a diagram showing a configuration example of the tape drive10, in accordance with one embodiment. As shown in FIG. 2, the tapedrive 10 includes a host interface (hereinafter called “host I/F”) 11, abuffer 12, a channel 13, a head 14, and a motor 15. The tape drive 10also includes a controller 16, a head position control system 17, and amotor driver 18. Since a tape cartridge 20 is loadable when the tapecartridge 20 is inserted into the tape drive 10, the tape cartridge 20is further shown here. This tape cartridge 20 includes a tape 23 woundon reels 21 and 22. The tape 23 moves in a longitudinal direction withthe rotation of the reels 21 and 22 from the reel 21 to the reel 22, orfrom the reel 22 to the reel 21. A magnetic tape is exemplified as thetape 23, but the tape 23 may be any magnetic medium other than themagnetic tape.

The host I/F 11 may communicate with the host (server) 30 or the otherterminals 32, 34. For example, the host I/F 11 may receive, from anoperating system (OS) of the host 30, a command to instruct writing ofdata to the tape 23, a command to move the tape 23 to a target position,and a command to instruct reading of data from the tape 23.

The buffer 12 may be a memory for accumulating data to be written to thetape 23 and data read from the tape 23. For example, the buffer 12 mayinclude a DRAM. The buffer 12 may be composed of multiple buffersegments, and each buffer segment may store a data set as a unit ofread/write from/to the tape 23.

The channel 13 is a communication channel that may be used to send thehead 14 data to be written to the tape 23 and receive, from the head 14,data read from the tape 23. The head 14 may write information to thetape 23 and read information from the tape 23 when the tape 23 moves inthe longitudinal direction. The motor 15 may drive the reels 21 and 22to rotate. Although the motor 15 is illustrated as a singular motor inFIG. 2, it may be preferable to provide, as the motor 15, two motors,such as a motor for each of the reels 21 and 22.

The controller 16 may control the entire tape drive 10. For example, thecontroller 16 may control writing to the tape 23 and reading from thetape 23 according to the commands accepted at the host I/F 11. Thecontroller 16 may also control the head position control system 17 andthe motor driver 18. The head position control system 17 may track adesired wrap, where the wrap may include a group of multiple tracks onthe tape 23. When it is necessary to switch from one wrap to another,the head 14 may also need to be electrically switched. Such switchingmay be controlled by this head position control system 17.

The motor driver 18 may drive the motor 15. As mentioned above, if twomotors 15 are used, two motor drivers 18 may also be provided.

As shown in FIG. 2, the tape drive 10 is a physical tape drive forreceiving and reading/writing a tape cartridge 20. Of course, in otherembodiments the tape drive 10 may be a virtualized or virtual tapedrive. In such embodiments, the tape drive 10 may include a logicalconstruct, such as software, that appears to the host 30 as an actualtape drive. Data may be read from or written to logical volumes of thetape drive 10, whether an actual tape drive or a virtual tape drive,through a read/write channel as is well known to those skilled in theart.

In embodiments employing a virtual tape drive, logical volumes may bestored on different physical media, including, but not limited to,storage cartridges, disk drives, solid state disks (SSD), disks directaccess storage devices (DASD), magnetic tape drives, libraries, and diskdrive arrays, such as RAID (redundant array of independent disks), JBOD(just a bunch of disks). An example of a storage cartridge is a magnetictape cartridge, which includes a rewritable magnetic tape wound on a hubof reel, and a cartridge memory. One example of a magnetic tapecartridge includes a cartridge based on LTO (Linear Tape Open)technology. Utilizing a virtual tape drive may allow access to logicalvolumes at disk speeds while maintaining compatibility with existingtape operations.

For simplicity, the instant description may describe methods and systemsas utilizing a tape drive. It is understood that the tape drive utilizedby these methods and systems is intended to include both actual tapedrives and virtual tape drives. Thus, references to a “tape drive” areintended to include an actual tape drive, as well as software appearingto a host as a physical tape drive. Additionally, for simplicity, theinstant description may describe methods and systems as utilizing a tapevolume. It is understood that the tape volume utilized by these systemsand methods is intended to include tape cartridges, as well as logicalvolumes stored on different physical media that appear to a host asbeing mounted via a tape drive.

Various embodiments disclosed herein are desirably able to protect datastored on a tape volume from being overwritten as a result of rewindoperations performed during error recovery processes. Specifically, bydetermining a current tape position, it may be determined if a pendingwrite operation will be performed at an allowed location on a tapevolume, as will be described in further detail below.

Referring now to FIG. 3, a flowchart of a method 300 is shown accordingto one embodiment. The method 300 may be performed in any of theenvironments depicted in FIGS. 1-2, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 3 may be included in method 300, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 300 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 300 may be partially or entirely performed by atape drive. The processor, e.g., processing circuit(s), chip(s), and/ormodule(s) implemented in hardware and/or software, and preferably havingat least one hardware component may be utilized in any device to performone or more steps of the method 300. Illustrative processors include,but are not limited to, a central processing unit (CPU), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), etc., combinations thereof, or any other suitable computingdevice known in the art.

Further still, any one or more of the operations of method 300 may beimplemented in one or more tape drives using microcode embodiedtherewith. In some approaches, one or more of the operations of method300 may be implemented in a system having a processor and logicintegrated with and/or executable by the processor, the logic beingconfigured to perform the one or more operations of method 300. Itfollows that any of the approaches described herein may be applied tophysical and/or logical tape systems depending on the desiredembodiment.

Referring now to FIG. 3, method 300 begins with operation 302, at whicha tape volume is mounted. The tape volume may be mounted due to anycommand that is associated with a mount command. For example, the tapevolume may be mounted as a result of a read command, write command,etc., which may come from a host, computer, etc. In one embodiment, thetape volume may be a volume on a physical tape that is mounted by anactual tape drive. In another embodiment, the tape volume may be avolume on a virtual tape drive.

After mounting the tape volume at operation 302, data is written to thetape volume at operation 304. The data written to the tape volume atoperation 304 may include any data, such as, for example, user data orsystem data. Further, the data written to the tape volume may bereceived from a host, such as from an application executing on the host.

Further, at operation 306, a determination is made as to whether anerror has occurred while writing the data to the tape volume. In oneembodiment, the error may comprise any error that results in a recoveryprocess that includes a rewind of the tape volume. For example, theerror may include a channel-type issue. Thus, at operation 306, it maybe determined whether an error has occurred that will result in the tapevolume being rewound. In some embodiments, error codes and/or unitchecks may be utilized to determine whether an error has occurred at thetape drive. Examples of such errors include channel errors, such as onthe read/write channel 13. In one embodiment, the error detected atoperation 306 may comprise an interface control check, which mayindicate that an incorrect signal has occurred on a channel path.

When an error has been detected at operation 306, the tape drive mayremain at the location on the tape volume where the error was detecteduntil any further instructions are received. For example, host recoveryefforts and/or system software may determine which, if any, post-erroroperations the tape drive is to perform.

In one embodiment, the tape drive may notify a host of the errordetected at operation 306. The notification may be in the form of a unitcheck sent from the tape drive. Moreover, in some approaches, the unitcheck may include a fault system code that includes a system messageindicating the cause of the detected error.

If, at operation 306, it is determined that an error has not occurred,then data continues to be written to the tape volume.

However, if, at operation 306, it is determined that an error hasoccurred, then error recovery is initiated at operation 310. Errorrecovery may include any predetermined method, such as preprogrammedinstructions, or a determined on-the-fly method to rectify the errordetected at operation 306. In some embodiments, initiating errorrecovery at operation 310 may include error recovery code gainingcontrol of the tape drive as a result of the detected error. The errorrecovery code may be a part of an OS of the host, such that errorrecovery code of the host's OS may gain control of the tape drive inresponse to a unit check from the tape drive.

In one embodiment, the error recovery initiated at operation 310includes the tape drive receiving one or more commands from a host. Forexample, the tape drive may receive one or more commands from the errorrecovery code on the host, as set forth in more detail below.

Next, at operation 312, a positional indicator is received by the tapedrive. In one embodiment, a host passes the positional indicator to thetape drive. In such an embodiment, the positional indicator may bepassed to the tape drive from software on the host. For example, thepositional indicator may be passed to the tape drive from the recoverycode of the host's OS. The positional indicator may include any valuethat the tape drive may use to identify a relative or absolute positionon the mounted tape volume. In some embodiments, the positionalindicator may include a relative or absolute position of a write head inrelation to the tape volume. For example, the positional indicator mayinclude a logical address, or a linear position (LPOS) value and/or ahorizontal position (HPOS) value. Moreover, the positional indicator mayinclude a block identifier, or address in the form of a bit value, hexvalue, etc. Still yet, the positional indicator may include a value thatis relative to another predetermined position of the tape volume, suchas a beginning of the tape volume, or an end of the tape volume. Inanother embodiment, the positional indicator may be determined by thetape drive based on a location of the error detected at operation 306.

In one embodiment, the positional indicator received at operation 312may indicate a position on the tape volume where the host will attemptrewriting a failed channel program. Thus, host software, such as errorrecovery code of the host's OS, may track write positioning on the tapevolume during write operation 304 for subsequently determining alocation at which an error detected at operation 306 has occurred.

Further, in various embodiments, the positional indicator may beincluded in a command that is passed from the host to the tape drive.For example, the positional indicator may be included in a channelcommand word. In one approach, the positional indicator may be a blockidentifier included in the channel command word.

In embodiments where the positional indicator is included in a commandthat is passed from the host, the command may be passed before anyrecovery rewind occurs. Passing the positional indicator ahead ofperforming recovery rewind may ensure that it is not possible to writeto the tape volume from the beginning of the tape volume, or from anyother position that is earlier than a position specified by thepositional indicator. If an issue were to occur and be undetected duringa tape rewind or tape repositioning, the tape may be positioned at anunexpected location without the error recovery code being aware of themistaken positioning. In such a scenario, if an application that iswriting data to the tape volume were to have additional buffers insystem memory ready to be written, and those buffers were written at theunexpected location, then data on the tape could be unintentionallyoverwritten, resulting in potentially catastrophic data loss.

Still yet, at operation 314, positional write protection is enabled. Inone embodiment, the positional write protection may be enabled inresponse to receiving the positional indicator received at operation312. In another embodiment, the positional write protection may beenabled in response to the error recovery initiated at operation 310.Further still, the positional write protection may be enabled inresponse to a combination of receiving the positional indicator receivedat operation 312 and initiating the error recovery at operation 310. Inyet another embodiment, the positional write protection may be enabledin response to an enabling command received from a host.

The positional write protection may be enabled at the tape drive.Further, the positional write protection may be a temporary writeprotection that is enabled on the tape drive for a finite period oftime, and which prevents writing to the tape volume at one or moreregions of the tape volume.

After the positional write protection is enabled at operation 314, themounted tape volume is repositioned at operation 316. In one embodiment,repositioning the tape volume at operation 316 may include rewinding thetape volume to a specific point on the volume. In another embodiment,repositioning the tape volume at operation 316 may include rewinding thetape volume to a known position, such as a beginning of the tape volumeor a load point, and then positioning the tape volume out to a givenposition. The given position may include a point on the tape volume thatis subsequent to the beginning of the tape volume or the load point, andat which a failed channel program should be retried. In this way, thetape drive may retry a failed channel program at a given position on arepositioned tape volume.

In one embodiment, the error recovery code of the host may provideinstructions or commands to the tape drive for rewinding the tape volumeand/or repositioning the tape volume.

In the various embodiments where an error has occurred on a channel,such as an interface control check, the tape volume may be rewound, andthen repositioned to where a failing channel program can be reissued orretried. When the tape volume is rewound, the tape volume may be rewoundto a known position, such as a load point. Further, the tape volume maybe repositioned back at the location the tape volume was at prior to theerror occurring. Thus, the tape volume may be repositioned to the sameblock identifier where an error occurred.

In embodiments employing a physical tape volume, this may includerewinding a physical tape, such as the tape 23 using the motor 15, to adesired position. In embodiments employing a virtual tape volume, thismay include repositioning a read/write head to a desired position of aphysical entity utilized in virtualizing the tape volume. Implementationof such embodiments may require converting a given logical or tapeposition to a meaningful position for interpretation by a controller ofthe virtual tape volume.

At operation 318 a host attempts to write data to the mounted tapevolume. In one embodiment, the tape drive may receive from the host atleast a portion of the failed data from the write operation 304 thatresulted in the detected error, so that the tape drive may attemptrewriting at least a portion of the data to the tape volume. Inparticular, the host may attempt to write at least a portion of the dataas a part of reissuing a failed channel program. In other words, thehost may attempt to reissue a failed channel program by, at least inpart, issuing a write command to the tape drive. Thus, the host mayagain attempt to write the data that it previously tried to write whenan issue occurred and an error was detected at operation 306. Further,the data that the host again attempts to write may be based on thedetected error.

In response to the host attempting to write the data at operation 318,the tape drive determines, at operation 320, whether a current tapeposition is greater than or equal to the positional indicator receivedat operation 312. For example, the tape drive may read a current tapeposition of the tape volume, and then compare the read position to thepositional indicator received at operation 312. As noted above, the tapedrive and/or the host may constantly track the current tape position.

Determining the current tape position may comprise determining a currentlocation of a magnetic medium storing the tape volume relative totransducers intended to perform a read or write command to the magneticmedium. For example, in an embodiment where the tape drive is an actualtape drive, determining the current tape position may includedetermining a current location of the magnetic tape relative totransducers intended to perform a read or write command. Thus, the“current tape position” may be the location where the writing requestedby the write command will be performed if allowed. As noted above, thecurrent tape position may be determined in any conventional manner, suchas by reading Linear Position (LPOS) data from the servo tracks of thetape, determining a block identifier of the last written data blockand/or of the data block to be written, etc.

Accordingly, the current tape position may include a position on thetape volume, such as a block identifier, that would be written to inresponse to a write command, or would be read from in response to a readcommand.

If, at operation 320, it is determined that the current tape position isnot greater than or equal to the positional indicator received atoperation 312, then at operation 322 the write of operation 318 is notallowed. Thus, if the tape drive receives a write command when thecurrent tape position is earlier than a specified positional offset(e.g., at an earlier block identifier, etc.), the write command isfailed. The current tape position may be earlier than the specifiedpositional offset as a result of failing to properly reposition the tapevolume at operation 316. This may occur if the tape volume is notpositioned back out after a recovery rewind to a known position. Thecurrent tape position may be earlier than the specified positionaloffset as a result of a hardware failure. For example, if somethingprevents the tape volume from being rewound.

By way of a specific example, the current tape position may be at thebeginning of the tape volume due to a software or hardware issue, andthe beginning of the tape volume is earlier than the positionalindicator received at operation 312. Consequently, at operation 322, awrite operation is failed or disallowed based on the comparison, atoperation 320, of the current tape position to the previously receivedpositional indicator. Upon failing the write operation, the tape drivemay inform the host of the rejection.

In this manner, data is prevented from being written to a tape volume ata location that is prior to a previously identified positionalindicator, and data previously written to the tape volume is kept intactin the event of a repositioning failure during a recovery process.

However, if at operation 320, it is determined that the current tapeposition is greater than or equal to the received positional indicator,then at operation 330 the data of operation 318 is allowed written. Asnoted above, this data may include data from a failed channel program.Accordingly, data from previously failed channel program may be writtento the tape volume only when the current tape position is greater thanor equal to the previously received positional indicator (e.g., blockidentifier, etc.). By ensuring that the data from the previously failedchannel program is only written when the current tape position isgreater than or equal to the previously received positional indicator,otherwise undesirable overwrite of data the on the tape volume may beprevented.

Further, in response to determining that the write is allowed atoperation 330, positional write protection is then disabled at operation332. Disabling the positional write protection at operation 332 mayallow a controlling device or host to continue to write to the mountedtape volume. In view of the above, a temporary position-based soft WORMenablement mechanism may be triggered by a recovery and/or rewind duringa recovery process.

Referring now to FIG. 4, a diagrammatic representation of a tape volume400 is shown, in accordance with one embodiment. As an option, the tapevolume 400 may be implemented in conjunction with features from anyother embodiment listed herein, such as those described with referenceto the other FIGS. Of course, however, such tape volume 400 and otherspresented herein may be used in various applications and/or inpermutations which may or may not be specifically described in theillustrative embodiments listed herein. Further, the tape volume 400presented herein may be used in any desired environment.

In one embodiment, the tape volume 400 may be on a tape cartridge thathas been inserted into an actual tape drive. In another embodiment, thetape volume 400 may comprise a virtualized tape. As noted previously, insuch an embodiment, logical volumes may be stored on different physicalmedia, including, but not limitedto, storage cartridges, disk drives, dstate disks (SSD), disks direct access storage devices (DASD), magnetictape drives, libraries, and disk drive arrays, such as RAID (redundantarray of independent disks), or JBOD (just a bunch of disks). Further,it is understood that the diagrammatic representation of the tape volume400 of FIG. 4 is simplified for aiding in the present disclosure.

Additionally, as illustrated in FIG. 4, data 402 is laid out on the tapevolume 400 in a write direction. The write direction may comprise adirection in which data is appended to the tape volume 400 by a tapedrive. Accordingly, the tape volume 400 includes previously written data402, as well as unwritten region 404. During writing of the data 402, anerror may be encountered that results in initiation of error recovery.For example, an interface control check may be encountered, and recoverylogic may be initiated in response to encountering the interface controlcheck.

As a part of the recovery logic, a positional indicator for a firstposition 410 on the tape volume 400 may be received the tape drive.Further, after receiving the positional indicator for the first position410, write protection may be enabled for the tape volume 400, and thetape volume 400 may be repositioned with respect to a write head of thetape drive. As a result of enabling write protection, the positionalindicator for the first position 410 may be used by the tape drive toprevent the writing of data to any location on the tape volume 400 thatprecedes the first position 410.

In one embodiment, the positional indicator for the first position 410may include a block identifier that coincides with the first position410 on the tape volume 400. Further, in such an embodiment, the recoverylogic may attempt to retry a failed channel program on the tape volume400. More specifically, the recovery logic may attempt to rewrite thedata to the tape volume 400 that resulted in the encountered error.

In some scenarios, the repositioning of the tape volume 400 may notsuccessfully reposition the tape volume 400 with respect to the writehead of the tape drive. In other words, the repositioning of the tapevolume 400 may result in the write head of the tape drive being locatedat a block identifier of the tape volume 400 that is earlier than wherethe channel program is to be retried. Further, the recovery logic maynot be aware of the positioning problem.

In response to the recovery logic retrying the failed channel program onthe tape volume 400, the tape drive may compare a current position ofthe tape volume 400 to the previously received positional indicator ofthe first position 410. If the current position of the tape volume 400is greater than or equal to the previously received positional indicatorof the first position 410, then the tape drive will allow the retriedchannel program.

However, if the recovery logic were to send data to be written to thetape volume 400 when a write head of the tape drive is located at secondposition 408, which would be associated with a block identifier that isearlier than the block identifier that coincides with the first position410, the write by the host would be disallowed. Thus the tape drive mayuse the positional indicator to prevent a host from inadvertentlyoverwriting data during a recovery operation.

The various embodiments described above preferably include drivemicrocode that is able to determine a current location on a tape volume.Moreover, the microcode is able to compare the determined currentlocation on the tape volume with a previously received positionalindicator, and disallow any received write commands that would result ina write to the tape volume that is earlier than positional indicator inorder to protect data previously written to the tape volume from beingoverwritten.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a FPGA, etc. By executable by theprocessor, what is meant is that the logic is hardware logic; softwarelogic such as firmware, part of an operating system, part of anapplication program; etc., or some combination of hardware and softwarelogic that is accessible by the processor and configured to cause theprocessor to perform some functionality upon execution by the processor.Software logic may be stored on local and/or remote memory of any memorytype, as known in the art. Any processor known in the art may be used,such as a software processor module and/or a hardware processor such asan ASIC, a FPGA, a central processing unit (CPU), an integrated circuit(IC), a graphics processing unit (GPU), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. An apparatus-implemented method, comprising:detecting an error while writing data to a tape volume on a tape;repositioning the tape in response to detecting the error; determining,based on a current position of the tape after the repositioning, whethera rewrite of data associated with the error to the tape volume isallowed; and rewriting the data to the tape volume in response todetermining that the rewrite of data associated with the error to thetape volume is allowed.
 2. The method of claim 1, wherein the errorincludes an interface control check.
 3. The method of claim 1,comprising receiving a positional indicator prior to repositioning thetape.
 4. The method of claim 3, comprising enabling positional writeprotection in response to receiving the positional indicator, whereinthe positional write protection is enabled prior to repositioning thetape.
 5. The method of claim 1, wherein the current write positioning onthe tape volume is tracked.
 6. The method of claim 1, wherein the atleast a portion of the data for rewriting is received from a host. 7.The method of claim 6, wherein the at least a portion of the data isreceived from recovery code of the host, and wherein the at least aportion of the data is based on the detected error.
 8. The method ofclaim 1, wherein the rewriting to the tape volume comprises retrying afailed channel program.
 9. The method of claim 8, comprising receiving apositional indicator prior to repositioning the tape, wherein retryingthe failed channel program is performed in response to determining thatthe current position of the tape is greater than or equal to thepositional indicator.
 10. The method of claim 9, wherein the positionalindicator comprises a first block identifier of the tape volume, and thecurrent position comprises a second block identifier of the tape volume.11. The method of claim 1, comprising enabling positional writeprotection in response to receiving a positional indicator, wherein thepositional write protection is enabled prior to repositioning the tape;and comprising disabling the positional write protection in response toallowing the rewriting of the data to the tape volume.
 12. The method ofclaim 11, wherein rewriting the data to the tape volume is disallowed inresponse to determining that the current position of the tape is lessthan the positional indicator.
 13. The method of claim 1, whereinrepositioning the tape for recovering from the error includes rewindingthe tape volume.
 14. The method of claim 1, wherein repositioning thetape for recovering from the error includes repositioning the tape outto a known position in the volume.
 15. The method of claim 1, whereinthe tape volume comprises a logical volume stored on a tape cartridge.16. The method of claim 1, wherein the tape volume comprises a logicalvolume stored on a physical medium that appears to a host as beingmounted via a tape drive.
 17. A computer program product for protectingoverwrite of a tape volume, the computer program product comprising acomputer readable storage medium having program instructions embodiedtherewith, the program instructions executable by a controller to causethe controller to perform a method comprising: detect, by thecontroller, an error while writing data to a tape volume; reposition thetape in response to detecting the error; determine, by the controller,based on a current position of the tape after the repositioning, whethera rewrite of data associated with the error to the tape volume isallowed; and rewrite, by the controller, the data to the tape volume inresponse to determining that the rewrite of data associated with theerror to the tape volume is allowed.
 18. An apparatus-implementedmethod, comprising: detecting an error while writing data to a tapevolume; receiving a positional indicator; repositioning the tape inresponse to detecting the error; determining a current position of thetape after the repositioning; and determining whether a rewrite of dataassociated with the error to the tape volume is allowed based on acomparison of the current position of the tape to the positionalindicator.
 19. The method of claim 18, comprising rewriting the data tothe tape volume in response to determining that the rewrite of dataassociated with the error to the tape volume is allowed.
 20. The methodof claim 18, comprising enabling positional write protection in responseto receiving the positional indicator, wherein the positional writeprotection is enabled prior to repositioning the tape, and comprisingdisabling the positional write protection in response to allowing therewriting of the data to the tape volume.